Distributed Systems: Networking Concepts PDF - Computer Networks

Distributed Systems Networking and internetworking From Coulouris, Dollimore, Kindberg and Blair Distributed Systems: Concepts and Design Edition 5, © Addison-Wesley 2012 1 Introduction  A network is a collection of computers and other devices...

Distributed Systems Networking and internetworking From Coulouris, Dollimore, Kindberg and Blair Distributed Systems: Concepts and Design Edition 5, © Addison-Wesley 2012 1 Introduction  A network is a collection of computers and other devices that can send and receive data between each other.  Each machine on a network is called a node.  Nodes that are use the network for communication purposes is called host.  Every network node has an address which is a series of bytes that uniquely identify it.  Addresses are assigned differently on different kinds of networks. 2 Introduction  An internetworking is the process or technique of connecting different networks by using intermediary devices such as routers or gateway devices.  Internetworking ensures data communication among networks owned and operated by different entities using a common data communication and the Internet Routing Protocol (IRP). 3 Introduction  The networks used in distributed systems are built from a variety of ‣ Transmission media (wire, cable, fiber and wireless channels) ‣ Hardware devices (routers, switches, bridges, hubs, repeaters and network interfaces) ‣ Software components (protocol stacks, network device drivers)  The resulting functionality and performance available to distributed system and application programs is affected by all these. 4 Introduction  A communication subsystem: the collection of hardware and software components that provide the communication facilities for a distributed system.  Example: the Internet is a single communication subsystem providing communication between all of the hosts that are connected to it.  The Internet is constructed from many subnets.  A subnet is a unit of routing; it is a collection of nodes that can all be reached on the same physical network. 5 Networking issues for distributed systems  Performance  The network performance is effected by some parameters that are of are affecting the speed of message transmission between interconnected computers. These parameters are:  Network Latency: the delay that occurs after a send operation is executed before data starts to arrive at the destination computer. ✓Measured as the time required to transfer an empty message ✓Determined primarily by software overheads, routing delays,...  Data Transfer Rate: the speed at which data can be transferred between two computers in the network once transmission has begun, usually in bits per second. ✓Determined primarily by the network physical characteristics 6 Networking issues for distributed systems  Following the previous definitions, the time required for a network to transfer a message containing length bits between two computers is: Message transmission time = latency + length/data transfer rate  The above equation is valid for messages whose length does not exceed the maximum that is determined by the underlying network technology.  Longer messages have to be segmented and the transmission time is the sum of the times for the segments.  Many of the messages transferred between processes in distributed systems are small in size; latency is therefore often of equal or greater significance than transfer rate in determining performance. 7 Networking issues for distributed systems  Scalability  Difficult to estimate the real size nowadays  The potential future size of the Internet  will be of order of the population of the planet  several billion nodes and hundreds of millions of active hosts  Reliability  Many applications are able to recover from communication failures and hence do not require guaranteed error-free communication  usually errors due to  software errors in sender or receiver  (for example, failure by the receiving computer to accept a packet)  buffer overflow  network errors (not that often though) 8 Networking issues for distributed systems  Security  firewall technology  cryptographic technology  Mobility  The Internet’s mechanisms have been adapted and extended to support mobility, but the expected future growth in the use of mobile devices will demand further development  Quality of Service  multimedia data transmission  Multicasting (one-to-many communication)  simultaneous transmission of messages to several recipients 9 Types of Network  Personal area networks, local area networks, wide area networks, metropolitan area networks.  Internetworks: networks composed of many interconnected networks (of the above types), integrated to provide a single data communication medium. 10 Personal Area Networks (PANs) 11 Local Area Networks (LANs) 12 Wide Area Networks (WANs) 13 Metropolitan Area Networks (MANs) 14 Wireless Network  Metropolitan area networks (MANs)  based on the high-bandwidth copper and fiber optic cabling  distances up to 50 km  technology ranging from Ethernet to ATM (Asynchronous Transfer Mode)  Wireless local area networks (WLANs)  IEEE 802.11 standard (WiFi) (a, b, and now g)  bandwidth near 54Mbps) - over 150m  Wireless metropolitan area networks (WMANs)  IEEE 802.16 WiMAX standard  Wireless wide area networks (WWANs)  GSM (3G, 4G); UMTS (Universal Mobile Telecommunication System)  rates up to 100 Mbps 15 Network Principles  Network interconnection is essential to ensure the scalability and openness of distributed systems.  The integration of local and wide area networks can provide each specific group of users with the necessary networking capabilities.  In global networks, information from one node to another is transmitted, as a rule, through transit nodes.  This process is called switching. Thus, the interconnection of networks is carried out through the use of switching nodes - routers, gateways, etc., as well as a layer of software that supports global addressing and data transmission to computers of the interconnected networks. 16 Network Principles  The principles on which computer networks are based include, in addition to packet switching, the use of a layered model of network protocols, routing, and support for the streaming model of data transmission.  The networking technique enables the integration of various heterogeneous networks.  The addressing and routing schemes used on the Internet are highly scalable.  They are constantly being revised to accommodate new application requirements for mobility, security and quality of service. 17 Network Principles  Switching?  Networks are used to interconnect many devices.  Since the invention of the telephone, circuit switching has been the dominant technology for voice communications.  Since 1970, packet switching has evolved substantially for digital data communications. It was designed to provide a more efficient facility than circuit switching for burst data traffic. 18 Network Principles  Packet switching  Packet switching technique (developed in 1960s)  Packet switching is a method of transferring the data to a network in form of packets.  In order to transfer the file fast and efficient manner over the network and minimize the transmission latency, the data is broken into small pieces of variable length, called Packet.  Each packet contains Source and destination address using which they independently travel through the network.  In other words, packets belonging to the same file may or may not travel through the same path. 19 Network Principles  Packet Transmission 20 Network Principles  Data streaming  streaming : transmission and display of audio and video in real time  video stream requires  1.5 Mbps if data compressed  120 Mbps if data un compresses  channel from source to destination of a multimedia stream  predefined route  reserved set of resources  buffering where appropriate for smoothness  IPv6 includes features for real-time separate IP stream treatment 21 Network Principles  Switching Scheme  Four Kinds of switching methods typically used  Broadcast  Circuit switching  Packet switching  Frame relay 22 Network Principles  Switching Scheme 23 Network Principles  Switching Scheme : Circuit Switching 24 Network Principles  Switching Scheme : Packet Switching 25 Network Principles  Switching Scheme : Circuit vs Packet Switching 26 Homework 3  Read chapter 3 27